# Comparing scaled error

Say I have a regression technique (in my case I'm using ANNs) I am tuning on a data set. Say I am minimising a loss function that is not scale free, such as mean square error. Usually I would normalise the input and the output, perhaps by Feature scaling or standardisation, split my data in training, validation and test, and choose my hyper-parameters based upon performance on the validation set.

However, how can I compare the impact of two different normalisation schema? I am transforming the output as well as the input, so the scale of the output, when normalising by $$Y'=\frac{Y-\mu}{\sigma}$$ or by $$Y'=\frac{Y-Y_{min}}{Y_{max}-Y_{min}}$$ is different. Is it a matter of algebra and rearranging to get two comparable measures of error? I'm also intending to use a scale free measure of loss, such as the coefficient of determination, but I should really be optimising on the measure of loss I use to compare my results, correct (ie. no comparing the MSE of a solution found by minimising MAE etc.)?

The only issue I have with this is that the error tracked automatically as the model is trained, such as in the keras.model.history object is in the normalised scale, but I suppose that's only important for seeing convergence?